1. Field of the Invention
The present invention relates to a carrier control method using phase-pulse signals, which performs information transmission between a terminal equipment and a receiver, by establishing a plurality of channels having a predetermined phase width, respectively, in each cycle of an alternating current carrier wave of a commercial frequency on low-voltage distributing lines and the like, and by inserting the phase-pulse signals in these channels.
2. Description of the Prior Art
This carrier control method is suited for automatically reading a watt-hour meter installed in each customer facility and for the centralized control of the loads carried by the customers. In the prior art of automatic meter reading by this method, a terminal equipment transmits one phase-pulse upon each unit of energy consumption by the customer, and a receiver counts the phase-pulses and memorizes the result as an automatically readable read value. In this case, however, since the read value is not stored in the terminal equipment, but one phasepulse is transmitted every time a unit amount of energy is consumed, the phase-pulses per unit amount of consumption by individual customers which are generated at random might be frequently transmitted when the conditions of the distributing lines are bad (for example, the loads are too large, adverse noise due to switching on the lines), causing transmission failures. If errors are introduced into counting and memory of the read value in the receiver by the transmission failures, they are gradually accumulated over a long period, so that they cannot be automatically corrected. In order to prevent this, it is desirable that the read datum of electric energy be stored in the watt-hour meter or in the terminal equipment in the electrically readable state, so that the read datum may be transmitted when the conditions of the low-voltage distributing lines are good.
As a transmission method of the read datum by the phase-pulse signals, as shown in FIG. 1, there exists a method in which a phase-pulse signal P.sub.1 composed of a start signal and a terminal address code is established by superposing one phase-pulse 2 on one cycle of an alternating current carrier wave 1, and by using a plurality of cycles, and where the phase-pulse signals P.sub.1 is sent to a terminal equipment, and in which the selected terminal equipment uses the plural cycles so as to return back a phase-pulse signal P.sub.2 of a returning datum. However, this method has its transmission delayed, and requires an error control, such as a transmission reference, especially in the case of any transmission lines of bad quality, so that its application is limited due to its transmission speed and its complicated construction of devices. As shown in FIG. 2, therefore, there has been developed by way of the present application a method, now issued as U.S. Pat. No. 4,179,624, in which channels C.sub.1 to C.sub.20 are established in the low-noise region of one cycle of the alternating current carrier wave 1, such that the channels C.sub.1 to C.sub.8 are assigned to terminal selection channels A.sub.1, the channels C.sub.9 and C.sub.10 to figure selection channels A.sub.2, and the channels C.sub.11 to C.sub.20 to returning channels A.sub.3, corresponding to the decimal numbers 0 to 9.
According to this method, however, since, in the case of the distributing lines, the channels cannot be established in one cycle of the alternating current carrier wave 1, except in the vicinity of a zero point having few noise perturbations, the width of one channel is narrowed, if the terminal selection channels A.sub.1, the figure selection channels A.sub.2 and the returning channels A.sub.3 are so fashioned as to have one hundred or more terminals for one line from a practical requirement of the automatic reading operation or the like.
As a result, that channel may possibly be influenced by the succeeding oscillations of the signal of the preceding channel. Especially, the phase-pulse signals for selecting the terminals and the figures are inserted at the receiver so that they have a remarkably high level at the receiver, but the returning phase-pulse signal to be returned back from the terminal on the returning channel A.sub.3 has a low level, because it has been attenuated while it is being sent from a distance.
It therefore takes a considerable time period for the succeeding oscillations of the terminal and figure selection phase-pulse signals having high levels to be attenuated to the low level of the returning phase-pulse signal. On the other hand, if the receiving threshold level of the receiver is lowered to match the level of the returning phase-pulse signal, the returning datum may be influenced to deviate by the succeeding oscillations of the terminal figure selection phase-pulse signals.